1. Field of the Invention
The present invention relates to microgyrometers achieved from a structure vibrating along a first direction.
2. Discussion of the Related Art
The principle on which microgyrometers are based is that, when the structure vibrating along a first direction is rotated about an axis orthogonal to the vibration direction, the vibrating structure tends to generate, due to the effect of the Coriolis acceleration, a vibration along a second direction, orthogonal to the first vibration direction and to the direction of the rotation axis. This induced vibration has an amplitude proportional to the rotation speed about the rotation axis.
It is clear that, to be adequately detected, the induced vibration should have a sufficient amplitude, i.e., the mass moving in vibration must be suspended so as to sufficiently vibrate in its plane along the first direction and along the orthogonal direction where the induced vibration is liable to occur. In addition, to prevent induced vibrations from occurring even in the absence of rotation, the natural resonance frequency along the first direction, at which the first vibration is excited, should be distinct from the natural vibration frequency along the orthogonal direction although these two frequencies should be close so as to obtain a vibration induced at the first frequency along the second direction when rotation occurs.
For the operation of the gyrometer, various actuators and sensors are associated with the vibrating mass preferably in the form of capacitors having one electrode formed on the vibrating mass and another electrode on a facing fixed surface. If x designates the first direction along which a vibration is generated and y designates the second direction along which an induced vibration should be detected, the following elements can be provided:
a first set of capacitors whose electrode plates are directed orthogonally to direction x, for drawing the vibrating mass in vibration at its natural frequency, (a piezoelectric excitation can also be used), PA1 a second set of capacitors whose electrode plates are directed orthogonally to direction x, for detecting and servo-controlling the vibration along axis x, PA1 a third set of capacitors whose electrode plates are directed orthogonally to direction y, for detecting the induced vibration, PA1 a fourth set of capacitors whose electrode plates are directed orthogonally to direction y, for servo-controlling and canceling an axis shift effect, and PA1 a fifth set of capacitors whose electrode plates are directed orthogonally to direction y, for ensuring a feedback enlarging the band width and stabilizing the gain.
It should be noted that at least some of these sets of capacitors should have a sufficient surface either to ensure a sufficiently efficient electrostatic excitation or a sufficiently sensitive detection.